This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Stu1p is an essential microtubule-binding protein in Saccharomyces cerevisiae, and functions as a regulator of mitotic spindle structure. It is a homolog of the CLASP family of microtubule plus end tracking proteins in metazoans. CLASP family binding partners have been identified in metazoans, but Stu1p's binding partners are unknown. We are trying to determine if Stu1p interacts with other proteins involved in mitosis, particularly in mitotic spindle integrity. Stu1p is also a phospho-protein, but the kinase(s) that phosphorylate it are unknown. We are attempting to identify all phosphorylated residues of Stu1p, as well as determine the kinases responsible for this phosphorylation and if phosphorylation is a regulator of Stu1p function.